The following was included as a leaflet with some other period literature issued by the Allard Motor Company, 51 Upper Richmond Road, Putney, LONDON SW15. Allard were appointed sole worldwide distributors for the Shorrock supercharger in 1961.
“Questions and Answers to often asked questions”
• What actually is supercharging?
The function of a supercharger is to allow a larger quantity, by weight of petrol-air mixture to be fed to the engine than could be induced in the normal way.
In other words, the engine receives its input of air at a pressure higher than atmospheric pressure, which is virtually equivalent to increasing the swept volume of the engine.
Thus, an engine of 1500 c.c. capacity supercharged at a pressure of 5 lbs./sq. in. has the same effective capacity as an engine of 2000 c.c. swept volume, since it is receiving its charge at atmospheric pressure (14.74 lbs./sq. in.) plus 5 lbs./sq. in. or at approximately one third greater pressure.
To obtain the fullest benefit, it is necessary to employ a supercharger which itself will operate efficiently over a wide speed range with the minimum absorption of power.v
It is to this end that the SHORROCK supercharger was designed.
• Why are they not offered as optional equipment by the motor manufacturer?
All cars are produced with engines of specified basic ratings and a supercharger is considered to be an extra appliance for boosting the engine by pressure induction.
In our opinion, the many advantages now proved by supercharging should lead to even greater popularity in the future, which may induce motor manufacturers themselves to offer the appliance as an “optional”.
• In what other way does it improve performance?
The Shorrock installation provides substantially more power (up to 50%). It gives improved engine flexibility which means less gear changing at all times. Many more hills can be taken “in top” and all at higher speeds if necessary. Snappier “off-the- mark” acceleration is obtained and the increased power considerably raises the average cruising speed.
• What about fuel consumption, and do I need special grades?
If a supercharged car is driven normally, that is without taking advantage of the extra power for increased speed and top gear performance, then fuel consumption is not affected. By using the supercharger to its full effect, however, increase in fuel consumption is only to be expected. This varies from 10% to 15%. Measuring performance and economy, however, against bigger cars of higher basic rating, this small increase is comparatively negligible. 100 octane fuels should be used for maximum performance.
• Will fitting a supercharger impair the basic engine?
On the contrary, with low pressure charging as used by Shorrock, apart from increasing thermal efficiency, all cylinders operate with a mixture of equal strength. This even distribution gives a longer life to the engine and prevents local mixture starvation to any one cylinder, often a cause of inadequate lubrication on starting is also a common cause of bore wear. The Shorrock supercharger supplies all cylinders with a surplus of oil collected in the casing upon starting which provides upper cylinder lubrication when it is most needed.
• I thought superchargers were noisy?
The noise often associated with superchargers can be caused by pressure differences at the discharge port. The Shorrock vane type compressor has the advantage of reducing noise, the charge being compressed internally and there is no back flow of air when the port is uncovered.
• Will the supercharger fit any car, and are any modifications necessary?
This Shorrock “blower” can be fitted to most cars where the engine layout provides the necessary room. We publish a list of current cars suitable for the Shorrock installation. For older cars we will gladly advise as to suitability.
The complete installation can be fitted in approximately a day. A new carburettor, however is necessary which, together with manifold pipes, fitting brackets, pulleys and belts, is supplied inclusive with the Supercharger. Installation may be effected quite easily by any competent garage or owner driver. We recommend that standard “touring” plugs be replaced by the “sports” type, apart from this normally no other engine modifications are necessary for normal road use.
Finally, should you change your car, the Supercharger can be transferred providing the engines are of reasonably similar capacities.
• I believe they are good for high altitudes?
Indeed yes. Supercharging is the only means of compensating for the loss of power inevitable with lowered air density. Quite a feature, particularly for Continental touring and, of course, for the export market generally.
• What servicing does the supercharger require and what is its expected life?
The supercharger is fed with a small supply of oil for lubrication of the bearings. It is essential that the engine oil is kept clean and the lubricator cleaned every 5,000 miles. Apart from this, no servicing is required.
Providing the oil is kept clean and the supercharger unit is not over-revved, the unit will last the life of the average engine.
• Surely there must be a disadvantage in fitting a supercharger?
Well, the only disadvantage, if you can call it that, is that by increasing the filling of the cylinder under pressure, there will be inevitably more heat to dissipate. However, providing the engine is in good condition no harm will result.
• Is a supercharger worth the outlay?
If you mean the SHORROCK, yes. It’s a precision engineered job backed by twenty years of research in the Supercharger field and proved under the most exacting trials.
Bearing in mind that the average supercharger installation gives up to 30% increase in both maximum power and torque with a substantial increase from as low as 2,000 R.P.M., then it is excellent value for money in terms of B.H.P. for £ spent.
Ed’s note: This leaflet unashamedly sells the virtues of the Shorrock supercharger but the information it contains is, I feel, useful for those of us not au fait with the ‘mysteries’ of supercharging.
A useful website devoted to the Shorrock can be found here.
I’ve used the relevant section of this website to give some brief details of the history of Shorrock:
Chris Shorrock’s work on forced induction (supercharging) led to the formation in 1934, of Centric Superchargers Ltd (later spelt as one word: Centric-superchargers Ltd.) who, by 26th July 1935 were based at Bow lane in Preston.
In 1946 Centric-superchargers Ltd changed their name to Shorrock Superchargers Ltd, and in 1949 the company moved to “Moorlands” Garstang Road, PRESTON, Lancashire, where they stayed into the 1950s.
The company saw a number of changes over the following years, being based in various locations in the West Midlands, including Coventry, Willenhall, and eventually, by 1957, Wednesbury where they stayed until the 1960s. By August 1957, Shorrock had become one of the companies within the Rubery Owen Organisation.
In November 1959 Donald Healey was appointed as a B.M.C. Distributor for the company. Apart from T-Types, the Shorrock “blower” was a popular fitment to the Morris Minor and Austin Healey Sprite (and the Ford Anglia)
On the 1st July 1961, the Allard Motor Company, was appointed the sole worldwide distributor.